The cynomolgus monkey retina, in vivo, and the bovine retinal pigment epithelium (RPE) in vitro, will be irradiated with narrow bandwidth electromagnetic radiation (300-460 nm). The effects of this treatment will be evaluated by ophthalmoscopy, light and electron microscopy, the biochemical assays of cell metabolism. The amount of energy within the "blue" and UV-A regions of the spectrum required to damage the retina will be determined, the cell type and cell components which are affected will be determined, the progress of histological and biochemical changes after irradiation will be described, the influence of melanin on the response of RPE in culture will be studied, and the hypothesis that visual pigments are involved in the light damage process will be tested. These data will provide important information concerning the light-absorbing entity(ies), their locus within the retina, and possibly their subcellular distribution. With this information the risk of light damage to the human retina in various environmental situations can be assessed, the risk incurred by aphakic persons can be determined, and the understanding of the mechanism of light damage gained will open new routes of study to find methods of blocking or reversing the process of light damage.